The present invention relates to a jig and in particular to a holder for dies used in the drilling and threading of self-tapping screws.
Screws or fasteners having the capability of drilling a pilot hole and forming threads in a workpiece without the need to predrill are well known. Such screws and the dies by which they are made are illustrated in U.S. Pat. Nos. 3,395,603; 3,517,542; and 4,836,730. According to these patents a pair of dies are used to forge and drill the point into a desired configuration. Each of the dies is held in a jig comprising a solid parallelepiped body ground at its bottom to fit the die set pocket of the forming machine and is provided at its upper edge with a U-shaped cavity in one corner. The die is set up against one wall of the cavity, and a pair of wedges (one wide and one narrow) are inserted between the die and the other wall. The wedges are formed with mating inclined surfaces and with flat surfaces which abut up against the die and the face of the cavity wall, respectively. The abutting vertical surface of the die is formed with a laterally extending detent which fits within a conforming recess made in the abutting face of the narrow wedge. When the wedges are put in place the narrow wedge is arranged so that the horizontal projection fits within the recess of the die but is otherwise loose. The larger wedge is then placed in position and is screwed or bolted to the base. In this manner the wedges are secured tightly, one with the other, against the die, which prevents any vertical movement and ostensibly fixes the die in place.
The foregoing assembly does not, however, provide for security against movement of the die or even the locking wedges in a horizontal or sideways direction within the cavity. Such security, however, is necessary in order to maintain the die head extending from the base of the jig body to allow the screw blanks to be inserted for cutting. During high speed operation of the cutting apparatus, frequent downtime is required in order to reset the die wedges and the die to ensure for such security.
A further disadvantage of the known jig lies in the fact that it requires two wedges which have to be milled and ground to absolute tolerances to ensure the perfect fit. Another disadvantage lies in the fact that the jig is weakened by the need to thin the cavity walls in order to provide room for the two wedges.
It is, therefore, the object of the present invention to provide a holder for dies used in the formation of self-tapping screws which provide the necessary security against movement of the die and is more effective and has a longer life for use in the mass production of self-tapping screws. It is a further object of the present invention to provide a die which is simpler to manufacture, simpler to assemble, and which does not exhibit any of the above-mentioned disadvantages.
The foregoing objects and numerous advantages of the present invention will be apparent from the following disclosure.